Michael Stoney, 44, the governor of Low Moss prison, near Glasgow, was pulled over by police officers who spotted him with the handset at his ear.

He was driving his Vauxhall Astra Coupe when he was stopped in Viewpark, Lanarkshire, on May 5.

Stoney, of Dunblane, Perthshire, pled guilty by letter. He has been ordered to appear in person to be sentenced next month.

Motherwell Justice of the Peace Court also asked for proof that he could lose his job if he is disqualified from driving.

In January, the Low Moss prison boss stood shoulder to shoulder with Justice Secretary Kenny MacAskill at the opening of the £120million jail in Bishopbriggs.

Announcing a plan to cut the power to prisoners’ cells during the day to force them to work, he said: “Our job at Low Moss is not to punish people, that’s decided by the courts. Our job is to challenge people’s behaviour.”

The Scottish Prison Service yesterday said: “We do not comment on individual staff members.”